This is a slightly convoluted workaround, but you could use my app Showr. It lets you add any image to your home screen, and one of the actions it can perform is launching a web page of your choice when clicked.

You could add a Showr widget to your home screen, set it to use any Wikipedia icon of your choice (whether it's already saved to your phone, or by giving it the URL of an icon to download), and set it to launch Wikipedia (in your browser) when clicked. Showr is a free download from Google Play.